1. Field of the Invention
The present invention relates to a switching apparatus and, more particularly, to a switching apparatus for transferring an ATM (Asynchronous Transfer Model) cell input from an input port at each interface point to an output port at a desired interface point in accordance with header information of the cell.
2. Description of the Related Art
A great deal of attention has been paid to an ATM technique as a technique aiming at a high-speed transmission/switching technique. An ATM is a technique aiming at implementation of hardware for packet switching by transferring a fixed-length short packet called a cell which carries all sorts of information, thereby facilitating transfer/switching of information at a high speed. In order to realize an ATM communication network for performing communication of information by using this scheme, it is essential to use a switching apparatus for transferring a cell from a given transmission line to a desired transmission line in accordance with the header information of the cell.
In conventional switching apparatuses, however, the following problems are posed. For example, in a conventional switching apparatus disclosed in U.S. Pat. No. 5,274,641 by one of the present inventors, dedicated hardware components for realizing the functions of physical and ATM layers are arranged along a data flow in a channel. The array of these dedicated hardware components connected in series perform physical and ATM layer function handling by a so-called pipeline scheme, in which each hardware component processes a data string received from the preceding hardware component. In a switching apparatus having such an arrangement, since the function of each layer is realized by a dedicated hardware component, the throughput is high. However, the dedicated hardware component on each layer increases the cost. Especially, an increase in cost is too high to apply the above system to a communication system currently attracting considerable attention as an ATM-LAN, which is designed to offer transmission ability based on ATM cells to terminals existing in a relatively closer area, or a so-called low-speed interface such as a 6.3-Mbps interface or a 20-Mbps interface which is used to accommodate low-end PCs in an ATM communication network and expected to be in great demand in the future.
In addition, a function realized by hardware lacks flexibility with respect changes in specifications. The ITU-T (International Telecommunication Unit) is enthusiastically promoting the standardization of the specifications of ATM communication networks. However, the standardization has not been completed yet. New specifications are proposed one after another.
If the function of each layer is realized by hardware in this state, hardware must be newly designed every time the specifications are changed or new specifications are proposed. As a result, a large amount of hardware must be designed, and the whole cost of the system is increased.